Delivery of gene products via mesangial cells

ABSTRACT

Disclosed are methods that achieve i) site-directed delivery, ii) in situ amplification, and iii) sustained expression of an exogenous gene product within renal glomeruli. An exogenous gene, E. coli β-galactosidase, was introduced into cultured rat mesangial cells using a replication-defective retrovirus, and stable infectants were administered to a rat kidney via the renal artery. In the injected kidney, the engineered, cultured mesangial cells populated 40% of glomeruli site-specifically. The gene product was detected throughout a 14-week period of observation. In an alternative method, engineered, cultured mesangial cells were injected into a kidney subjected to an antibody that induces mesangiolysis followed by mesangial regeneration. Under these conditions, expression of β-galactosidase was dramatically amplified in situ, and high level expression continued for at least 8 weeks.

FIELD OF THE INVENTION

This invention relates to delivery of cultured mesangial cells to akidney of a mammal. More particularly, the invention relates to methodsof administering cultured mesangial cells via a renal artery, fromwhence the cells are transported to and accumulate specifically inglomeruli of the kidney. The invention further relates to methods ofexpressing an exogenous gene product from such administered mesangialcells.

BACKGROUND OF THE INVENTION

Glomerular disease is one of the major causes of chronic renal failure.During the past five years, it has been suggested that various moleculessuch as cytokines/growth factors and proteolytic enzymes may be involvedin the pathogenesis of glomerular injury as well as in the induction ofproteinuria. M. Kashgarian and R. B. Sterzel, Kidney Int. 41, 524(1992); W. H. Baricos and S. V. Shah, Kidney Int. 40, 161 (1991).However, many recent studies have used cultured cells or affectedtissue, and therefore do not generate an understanding of thepathological role of such molecules in the generation of injury in vivo.An important challenge in this field is to identify molecular mediatorspivotal in different types of glomerular damage, for example, throughuse of an appropriate in vivo system to select candidate molecules.Currently, there are no such methods appropriate for this purpose. Thus,it would be useful to establish methods suitable for assessing thepathophysiological function of specific molecules in situ., i.e., withinrenal glomeruli, using gene transfer technology.

The most commonly used techniques for delivering exogenous nucleic acidinto cells involve the use of viral vectors. These vectors areadvantageous in that they can infect large percentages of recipientcells and can integrate into the cell genome. The viral vectors areoften constructed to be replication-defective once they have transfecteda cell line. Other viral vectors that have been proposed or used fordelivering nucleic acid into cells include adenovirus, adeno-associatedvirus, herpes virus and poliovirus vectors. The retroviral andadeno-associated virus vectors are most often proposed or used for exvivo gene therapy, i.e., delivery of an exogenous DNA construct intocells temporarily removed from the body of the patient.

Hereinafter, exogenous nucleic acid construct or exogenous geneconstruct refers to a nucleic acid sequence originating outside arecipient cell and introduced into a recipient cell by a nucleic aciddelivery technique. A nucleic acid or gene construct may be manufacturedusing recombinant DNA technology known in the art, or may be a nucleicacid fragment purified from a source material without furthermanipulation. The exogenous gene may be entirely composed of homologoussequences, i.e., sequences cloned, isolated, or derived from the samespecies from which the recipient cells derive. Alternatively, all or aportion of the exogenous gene may be composed of sequences from speciesother than the species from which the recipient cells derive,hereinafter termed heterologous sequences. The exogenous gene constructmay be natural in that none of the regulatory sequences and codingsequences that may be a part of the gene are substantially orintentionally altered, or the exogenous gene construct may be chimericin that sequence fragments from various sources are present in the finalgene construct. Examples of exogenous nucleic acid constructs introducedinto cells include constructs expressing bacterial proteins, oncogenes,cell surface molecules, and antisense sequences. Minoru, S., et al.,EMBO J. 9:2835 (1990); Gossett, L., J. Cell Biol. 106:2127 (1988);Townsend, S. and Alison, P., Science 259:368 (1993); Trojan, J., et al.,Science 259:94 (1993).

Gene transfer has been effected into various organs including bonemarrow, skin, brain, heart, muscle, lung, liver, kidney, and arterialwall. J. W. Larrick and K. L. Burck, Gene Therapy: Application ofMolecular Biology (Elsevier, N.Y. 1991) chap. 5-7; H. Lin, et al.Circulation 82, 2217 (1990); R. J. Bosch, A. S. Woolf, L. G. Fine, Exp.Nephrol. 1, 49 (1993). In these cases, exogenous genes have been appliedto the target organ or tissue by direct injection or local instillationof materials. In the kidney, however, the glomeruli are small structures(100-200 μm in diameter) scattered throughout the renal cortex (3×10⁴-1×10⁶ glomeruli/kidney) and, therefore, cannot be targeted byconventional approaches. Direct injection of viral vectors orDNA-liposome complexes into the renal circulation potentially couldcause other renal cell types as well as other organs to be exposed tothe exogenous DNA.

Woolf et al., Kidney, Int. 43 (Suppl. 39): S116-S119 (1993) disclosedtwo approaches to gene therapy of the kidney. The first approachinvolved transplantation of embryonic metanephric tissue that had beentransduced with a reporter gene carried by a retroviral vector. Incontrast to adult tissue, the embryonic metanephros contains mitoticallyactive cells, required for integration and expression of the retroviralvector. Pieces of the transduced embryonic tissue were transplantedunder the renal capsule of adult mice or into the renal cortex ofneonatal mice. The authors admitted that long-term survival of themetanephric transplants was limited by ischemia and immune rejection.This approach is dependent on a source of compatible embryonic tissue,and requires surgical intervention in the patient's kidney.

The second approach involved direct injection of retrovirus vectors intokidneys of adult mice. A small number of proximal tubular cells werefound to express a reporter gene a few days after injection ofretrovirus. Such direct administration of virus creates the possibilityfor non-kidney tissues and organs to be exposed to the vector. Moreover,since retroviruses require dividing cells for integration and long-termexpression, Woolf et al. needed to create a proliferative environment inthe adult kidney. They accomplished this by treating the recipient micewith folic acid in order to create generalized and sub-acute damage tothe kidney. This, in turn, generated a round of repair proliferationthat facilitated integration of the retrovirus vectors. Woolf et al.pointed out that this approach "clearly . . . would be unacceptable ifgene transfer into human kidneys was contemplated, unless the injuryphase could be tightly controlled."

SUMMARY OF THE INVENTION

Disclosed herein is a method of introducing an exogenous gene into akidney of a mammal, comprising the steps of: providing a plurality ofcultured mesangial cells that are immunologically compatible with themammal and that contain a nucleic acid construct comprising theexogenous gene, and administering the construct-containing mesangialcells to the renal artery of the kidney under conditions where the cellsbecome entrapped in glomeruli of the kidney. The nucleic acid constructmay further comprise a replication-defective retroviral sequence and beintroduced into the cultured mesangial cells by transfection.

The exogenous gene may comprise a coding sequence for a gene product.The gene product may be expressed, secreted and enter the circulatorysystem, the interstitial space or urinary tract of the mammal, or thegene product may be expressed, secreted and be localized in the kidneyof the mammal or on the mesangial cell surface. The exogenous gene mayfurther comprise a Moloney murine leukemia virus long terminal repeat.The mesangial cells may be administered to one or both renal arteries ofthe mammal.

Another method of introducing cultured mesangial cells into a kidney ofa mammal comprises the steps of: providing a plurality of culturedmesangial cells that are immunologically compatible with the mammal andadministering the cultured mesangial cells to the renal artery of thekidney under conditions where the cells become entrapped in glomeruli ofthe kidney, and selectively damaging the in situ mesangial cells of thekidney with a mesangiolytic agent. Selectively damaging the in situmesangial cells may occur prior to or after the infusing step. Thecultured mesangial cells may contain a nucleic acid construct thatcomprises an exogenous gene. The mesangiolytic agent may comprise ananti-mesangial cell antibody, and may comprise an anti-mesangial cellmonoclonal antibody. A suitable mesangiolytic agent comprises themonoclonal antibody 1-22-3.

A method of introducing cultured mesangial cells into a kidney of amammal is disclosed, comprising the steps of: providing a plurality ofcultured mesangial cells that are immunologically compatible with themammal and administering the cultured mesangial cells to the renalartery of the kidney under conditions where the cells become entrappedin glomeruli of the kidney.

An article of manufacture comprising packaging material and a pluralityof cultured mesangial cells contained within the packaging material isdisclosed. The cultured mesangial cells are effective for administrationto a renal artery of a mammal under conditions where the cells becomeentrapped in glomeruli of the kidney and are immunologically compatiblewith the mammal. The packaging material contains a label or packageinsert indicating that the cultured mesangial cells can be administeredto the renal artery under conditions where the cells become entrapped inglomeruli.

The cultured mesangial cells contained within the packaging material maycontain a nucleic acid construct comprising an exogenous gene. Theconstruct-containing mesangial cells may comprise the cell lineRM4/BG715.

Also disclosed is an article of manufacture comprising packagingmaterial and a mesangiolytic agent contained within the packagingmaterial. The mesangiolytic agent is effective for selectively damagingthe in situ mesangial cells of a kidney of a mammal. The packagingmaterial contains a label or package insert that indicates themesangiolytic agent can be used for introducing cultured mesangial cellsinto the kidney of the mammal by steps comprising: providing a pluralityof cultured mesangial cells that are immunologically compatible with themammal, administering the cultured mesangial cells to the renal arteryof the kidney under conditions where the cells become entrapped inglomeruli of the kidney, and selectively damaging the in situ mesangialcells of the kidney with a mesangiolytic agent. The mesangiolytic agentmay be an anti-mesangial cell antibody, such as the anti-mesangial cellmonoclonal antibody 1-22-3.

DETAILED DESCRIPTION OF THE INVENTION

This invention describes a method of site-directed gene delivery toglomeruli of one or both kidneys of a mammal. In this method, renalglomerular mesangial cells are cultured and transfected outside of thebody so as to introduce a gene or genes of interest, and such cells arethen administered to a kidney via the renal artery. The administeredmesangial cells target glomeruli specifically, and a gene product isexpressed within glomeruli. The method may further involve subjecting akidney to an agent that induces mesangiolysis followed by mesangialregeneration. When engineered mesangial cells are infused into a renalartery supplying such a selectively damaged kidney, expression of anexogenous gene is dramatically amplified in glomeruli and the expressionis maintained for at least 8 weeks. Additionally, higher numbers ofglomeruli are found to have engineered mesangial cells present thanwould be expected from infusion of mesangial cells withoutmesangiolysis.

The present invention represents a novel method that may be used to i)transfer an exogenous gene into specific microscopic structures withinan organ, and ii) amplify the introduced gene and its product in situ ina site-specific manner. The method has several advantages compared withconventional in vivo gene transfer using viral vectors or liposomes,e.g., high efficiency, high site-specificity of gene delivery and stableexpression. This system allows sophisticated cell engineering to becarried out in vitro prior to injection, and enables the transfer ofmultiple genes in order to express multiple therapeutic gene products ormultiple metabolic pathway components from the glomeruli.

The method uses the renal glomerular mesangial cell for site-specificlocalization. In the rat glomerulus, the diameter of the capillariesranges from 5 to 25 μm (afferent arteriole: 25 μm). A. Remuzzi, et al.,Am. J. Physiol. 263, F562 (1992). The diameter of cultured rat mesangialcells is about 15-25 μm. When such mesangial cells are injected into therenal artery, the cells lodge or are entrapped within glomerularcapillaries. Thus, the site of gene introduction is restricted toglomeruli. In this way, glomeruli (100-200 μm in diameter) scatteredthroughout the renal cortex can be targeted. In humans, the diameter ofmesangial cells likewise is greater than the diameter of the glomerularcapillaries. See, e.g., Brenner and Rector (eds.) The Kidney, Vol. I,pp. 10-11 (1991). The present methods are site-specific, in contrast topossible alternatives that use direct injection of viral vectors orDNA-liposome complexes into the renal circulation. Alternative methodsexpose the entire renal vasculature as well as other organs to virusvectors or DNA-liposome complexes.

For purposes of the present invention, biopsies are taken from a kidney,and mesangial cells are isolated from the biopsy material. Exogenousnucleic acid constructs containing a desired gene or genes aretransfected into the isolated mesangial cells. These transfections, orintroductions of exogenous genes into the cells, are performed usingtechniques known to the skilled artisan.

The transfected mesangial cells are administered to a recipient kidneyvia the renal artery. Cells may be administered by any suitable means,such as infusion or injection. Cells preferably are administered byinjection. Because the diameters of the mesangial cells are similar toor less than the inner diameters of the afferent arterioles ofglomeruli, but larger than the capillaries within a glomerulus, injectedcells are entrapped within glomerular capillaries; entrapment is notdetected in other parts of the kidney or in other organs. As such, thetransfected mesangial cells populate glomeruli in a site-specificfashion.

Renal glomerular mesangial cells of the invention may be syngeneic,allogeneic, or xenogeneic. Preferred cells are syngeneic or allogeneic,in order to minimize the possibility of immune rejection phenomena. Inone embodiment, autologous cells are used in the methods of the presentinvention. That is, mesangial cells can be cultured from biopsy tissueof one kidney, transfected with a specific gene in vitro, and the stabletransfectants injected into the contralateral kidney of the samepatient. Alternatively, the transfected mesangial cells can even beadministered to the same kidney from which the original biopsy tissuewas taken. On the other hand, it is known that many immune rejectionphenomena may be controlled or otherwise suppressed by means known inthe art. Thus, even xenogeneic cells may be made immunologicallycompatible, if necessary, by controlling or otherwise suppressing anyimmune rejection that may occur when practicing the methods of theinvention.

An exogenous gene may comprise a coding sequence for a gene product,e.g., a polypeptide. A coding sequence for a gene product may be placedunder the control of regulatory elements to ensure effective productionof the substance. Regulatory elements may include promoters, repressors,enhancers, polyadenylation regions and the like. Regulatory elements arepositioned properly with respect to a coding sequence in order toachieve effective production of the gene product. Some regulatoryelements may need to be rather precisely positioned with respect to thecoding sequence, whereas the exact position is less restrictive forother regulatory elements. For example, promoters must be positioned 5'to a coding sequence in order to obtain proper initiation oftranscription. In contrast, enhancer elements may be active whenpositioned either 5' or 3' of a transcribed sequence. Majors, J. andVarmus, H., Proc. Natl. Acad. Sci. USA 80:5866 (1983); Chandler, V, etal., Cell 33:489 (1983); Ponta, H., et al., Proc. Natl. Acad. Sci. USA82:1020 (1985).

When an exogenous gene comprises a coding sequence for a gene product,the gene product may be expressed and may remain within the cell, i.e.,the gene product may be localized within the expressing mesangial cell.Furthermore, a gene product may be targeted to particular cytoplasmic ornuclear compartments of the mesangial cell. Alternatively, a geneproduct may be directed to the mesangial cell surface, or may besecreted or otherwise directed to other kidney cell types. Mesangialcells entrapped in the capillaries of glomeruli are ideally positionedto allow diffusion of secreted proteins throughout glomeruli via thecapillary lumen, endothelial fenestrae, and mesangial pathways. Thesepathways allow access for secreted therapeutic products to the systemiccirculation, the renal interstitium and the urinary tract. Entrappedcells should not compromise renal function since glomerular capillariesare complex networks with numerous inter-connections, comprising about400 capillary segments with 250 junctures per glomerulus. A Remuzzi, etal., Am. J. Physiol. 263, F562 (1992). A gene product also may bedirected to the circulatory system of the recipient mammal. Sequencesuseful for directing a gene product to particular cellular locations orto a secretory pathway are known in the art.

The methods of the invention may be used to perform somatic cell genetherapy by introducing therapeutic genes specifically into glomeruli ofthe kidney. Such an approach is useful for prevention or treatment ofsuch diseases as progressive sclerosis of renal glomeruli orproteinuria. Since mesangial cells become lodged in the vasculature, thecells may deliver polypeptides, DNA, RNA or other therapeutic substancesto the systemic circulation in addition to local delivery to the kidney.

Using this methodology, expression of an exogenous gene is detected onlyfrom glomeruli of the kidney immediately downstream of the injectionsite. Expression is not detected in the contralateral kidney or in otherorgans such as the lungs, where one might expect intravenously injectedcells to be entrapped if they had escaped from the kidney.

In an alternative embodiment, cultured mesangial cells are administeredto the renal artery of a kidney that has been subjected to an agent thatinduces transient mesangial regeneration. A mesangiolytic agent may beany agent that selectively damages in situ kidney mesangial cells, i.e.,those mesangial cells present in a recipient mammal prior toadministration of cultured mesangial cells. For example, ananti-mesangial cell antibody may be introduced into a recipient via thevenous circulation, damaging or killing at least some of the in situmesangial cells by antibody-dependent cell-mediated cytotoxicity (ADCC)or by natural killer cell mechanisms. A few days before or aftermesangiolytic agent treatment, cultured mesangial cells having a desiredexogenous gene construct are introduced into the kidney via the renalartery. Under these conditions, the present inventor has discovered thatexpression of an exogenous gene is dramatically amplified in situ andthat high level expression continues for extended periods of time. Thisphenomenon may at least partially reflect an increase in the number ofcultured mesangial cells present in the glomeruli.

In a third embodiment, cultured mesangial cells without an exogenous DNAconstruct are injected into a renal artery of a kidney. The mesangialcells may be tissue typed in order to correspond immunologically asclosely as possible to the kidney, by methods known in the art. Thesecells become entrapped in glomeruli of the kidney, repopulate in themesangium and begin to perform the normal functions of mesangial cells.Such cells therefore can be useful in treating kidney diseases in whichmesangial cells are deficient in number or in function.

The present inventors have observed histological evidence of glomerularinjury when reporter cells are injected into damaged and regeneratingglomeruli. This means that cultured mesangial cells behave quiescentlyin the normal environment of glomeruli but may exhibit sclerogenicproperties within regenerating glomeruli at least in some circumstances.Thus, transfer of mesangial cells into some forms of diseased glomerulimay accelerate the underlying injury. To eliminate this response, thepresent inventor has discovered that replication-defective (e.g.,mitomycin C-treated) but otherwise viable mesangial cells do not inducesuch glomerular injury. Thus, use of such cells can result in successfuldelivery of a foreign gene and its product into the nephritic glomeruluswithout injury due to the mesangial cells per se.

Mesangial cells are thought to be major factors in the pathogenesis ofglomerular disease. M. Kashgarian and R. B. Sterzel, Kidney Int. 41, 524(1992); W. H. Baricos and S. V. Shah, Kidney Int. 40, 161 (1991). Sinceglomerular damage and proteinuria induced by antibody is acute andreversible, the disclosed method of antibody treatment and mesangialcell injection offers a new chronic and progressive system of glomerularinjury for study of i) the inn vivo behavior of cultured mesangialcells, ii) phenotypic differences between mesangial cells within theglomerulus, and iii) underlying mechanisms of glomerular damage. H.Kawachi, et al., Clin. Exp. Immunol. 88, 399 (1992); H. Kawachi, et al,Clin. Exp. Immunol. 90, 129 (1992). The disclosed procedures are alsouseful for identifying specific gene products that can rescue theglomerulus from progressive sclerosis or prevent proteinuria.

The invention also provides a method for non-local (e.g., systemic)delivery of therapeutic products. This is because gene products releasedby the mesangial cells into the glomerular capillaries thereby gainaccess to the systemic circulation, the renal interstitium and theurinary tract, as described above.

The invention will be further understood with reference to the followingillustrative embodiments, which are purely exemplary, and should not betaken as limiting the true scope of the present invention as describedin the claims.

EXAMPLE 1 Site-Specific Delivery of Cultured Mesangial Cells to theKidney

A replication-defective retroviral vector, BAG, was used to introduce areporter gene into mesangial cells. J. Price, D. Turner, C. Cepko, Proc.Natl. Acad. Sci. USA 84, 156 (1987). This vector has an Escherichia coliβ-galactosidase coding sequence (Lac-Z) under the control of a Moloneymurine leukemia virus long terminal repeat and a neomycinphosphotransferase coding sequence (neo) under the control of a SimianVirus 40 early promoter. Beta-galactosidase activity was used as areporter for the location of administered mesangial cells, and the neogene product, which confers resistance to G418, was used as a selectablemarker.

BAG DNA was introduced by electroporation into a helper free ecotropicpackaging line, ΩE. J. P. Morgenstern, H. Land, Nuc. Acids Res. 18, 3587(1990). A viral stock having about 4.4×10⁴ χ-gal cfu/ml was preparedfrom the conditioned media of stable transfectants as described in C.Cepko, Methods in Neurosciences. (Academic Press, 1989) vol. 1, chap.21. The viral stock was tested and shown to be free of helper virus.

Mesangial cells were isolated and cultured from glomeruli of a maleSprague-Dawley rat (250 gm) by standard methods described in M.Kitamura, et al., Kidney Int. 40, 653 (1991). Dulbecco's modifiedEagle's medium (DMEM) containing 10% fetal calf serum was used as thecell culture medium. After 4 passages in culture, mesangial cells wereinfected with BAG virus. Stable transfectants were selected in thepresence of 500 μg/ml G418.

To identify a cell line expressing β-galactosidase, samples fromselected mesangial cell clones were fixed for 15 minutes at roomtemperature in phosphate buffered saline (PBS) containing 0.5%glutaraldehyde, 2 mM MgCl₂, and 1.25 mM EGTA. After washing repeatedlywith ice-cold PBS, cell samples were incubated at 37° C. for 2 hours inχ-gal solution. χ-gal solution contains 1 mg/ml5-bromo-4-chloro-3-indolyl β-D-galactopyranoside (Sigma), 5 mM K₃Fe(CN)₆, 5 mM K₄ Fe(CN)₆.3H₂ O, 2 mM MgCl₂, 0.01 % sodium desoxycholateand 0.02% Nonidet P40 in PBS (pH 7.4). A high β-galactosidase-expressingclone, RM4/BG715, was identified by this procedure and selected for usein the experiments described below. Non-transfected, cultured mesangialcells do not express β-galactosidase activity.

Clone RM4/BG715 was shown to be a mesangial cell clone by itsmorphological features and its reaction with three mesangialcell-specific immunological markers. RM4/BG715 cells were cultured onchamber slides and fixed with cold methanol. The cells in separatechamber slides were incubated at 4° C. overnight with one of the firstantibody preparations indicated below. Cells were then washed with PBS,and incubated with an FITC-conjugated second antibody at 37° C. for 1hour. Photographs were taken by fluorescence microscopy. Preparationsused as the first antibody were: rabbit anti-desmin anti-serum (Sigma;1:20 dilution), mouse anti-mesangial cell monoclonal antibody 1-22-3(1:20 dilution) and mouse anti-α smooth muscle actin monoclonal antibody(Sigma; 1:200 dilution). H. Kawachi, et al., Clin. Exp. Immunol. 88, 399(1992); H. Kawachi, et al, Clin. Exp. Immunol. 90, 129 (1992).Preparations used as the second antibody were FITC-conjugated goatanti-rabbit immunoglobulin (Sigma; 1:32 dilution), and FITC-conjugatedgoat anti-mouse immunoglobulin (Sigma; 1:50 dilution). Clone RM4/BG715showed "hill and valley" formation and positive immunofluorescencestaining for desmin, α smooth muscle actin and Thy 1-associated antigen,all of which are characteristics typical of cultured mesangial cells. Noreplication-competent virus was detected in the conditioned medium ofthis clone and no evidence of transformation was observed in this cellline in a soft agar colony-formation assay, performed according to themethods of Rizzino, Soft Agar Growth Assays for Transforming GrowthFactors and Mitogenic Peptides. In Methods in Enzymology, Peptide GrowthFactors, Part A (Barnes and Sirbasku, eds.), Academic Press (1987).

Adult male Sprague-Dawley rats (250-450g) were anesthetized with ahypnorm-diazepam mixture. The left kidney was exposed through a leftflank incision. The kidney was separated from the surrounding fattytissue and the adrenal gland, and positioned in a kidney cup. The renalartery was then exposed and separated from the renal vein. A cottonthread was passed around the proximal site of the renal artery, and therats were then left for about ten minutes before cell injection.Confluent RM4/BG715 cells (0.5-2.5×10⁶ cells, 7-17th passages) weretrypsinized, washed once, resuspended in 700 μl of DMEM and injectedinto the left renal artery using a 27-gauge needle (50-100 μl/sec). Toavoid bleeding after injection, the renal artery was clamped with athread for several minutes and then allowed to reperfuse.

Four of the injected rats were sacrificed at 4 hours. The remaining ratswere maintained for 1, 2, 4, 8 or 14 weeks, and two animals weresacrificed at each time period. Both kidneys were removed from theanimals, and a portion of each kidney was used for glomerular isolationand another portion was used for preparing frozen sections formicroscopy. For glomerular isolation, renal cortices were dissected,diced into small pieces, and forced through a 106 μm mesh screenfollowed passage through by a 180 μm mesh screen. The resulting filtratewas passed through a 64 μm mesh screen, and washed repeatedly with PBS.Glomeruli remaining on the 64 μm mesh screen were used for the χ-galassay described below. The purity of the isolated glomeruli was morethan 95% as judged by phase-contrast microscopy.

Renal tissues and isolated glomeruli were fixed at 4° C. overnight in 2%paraformaldehyde, 0.2% glutaraldehyde, 2 mM MgCl₂, and 1.25 mM EGTA in0.1M piperazine-N,N'-bis[2-ethanesulfonic acid] (PIPES) buffer (pH 6.9).Renal tissues were placed in 2 mM MgCl₂ and 30% sucrose in PBS andstored at 4° C. Cryostat sectioning of renal tissues was carried out byprocedures known in the art. Fixed glomeruli and fixed frozen renaltissue sections were washed repeatedly at 4° C. with PBS containing 2 mMMgCl₂, washed once with 2 mM MgCl₂, 0.01% sodium desoxycholate and 0.02%Nonidet P40 in PBS, and then incubated at 37° C. for 2 hours in theχ-gal solution described above. The percentage of glomeruli having ablue color, indicative of the χ-gal product of β-galactosidase activity,was determined.

The incubation time should be no longer than 2 hours because anendogenous β-galactosidase activity appears in glomerular macrophagesafter a 12 hour incubation and appears in tubular epithelial cells aftera 3-4 hour incubation. In a 2 hour incubation, only β-galactosidaseactivity due to injected mesangial cells was observed.

The percentage of χ-gal positive glomeruli at each time period is shownin Table 1. Injected, cultured mesangial cells were distributedthroughout the left kidney and accumulated specifically in glomeruli.Four hours after injection, 39.8% of the glomeruli stained positive inthe χ-gal assay. χ-gal positive glomeruli also were detected at 1, 2, 4,8 and 14 weeks after injection (Table 1). χ-gal staining was detectedonly in the glomeruli and not in other portions of the left kidney. Noχ-gal staining was detected in the contralateral kidney (Table 1), or inother organs such as the lungs (data not shown). Injection of aβ-galactosidase negative clone, RM4-4, did not result in any χ-galpositive staining in the glomeruli of injected kidneys (data not shown),indicating that the enzymatic activity observed with RM4/BG715-injectedrat glomeruli was derived from the exogenous β-galactosidase genepresent in RM4/BG715 cells. These findings show that cultured mesangialcells are entrapped specifically in renal glomeruli when injected into arenal artery. These findings also show that when an exogenous nucleicacid construct is introduced into cultured mesangial cells, a geneproduct from construct-containing cells is expressed in glomeruli afterinjection of such cells.

                  TABLE 1                                                         ______________________________________                                        Percentage of X-gal positive glomeruli in                                     left and right kidneys after RM4/BG715 cell injection                                                X-gal positive                                                  Time          glomeruli (%)                                                     after           Left  Right                                        Animal     Injection       Kidney                                                                              Kidney                                       ______________________________________                                        1          4     hr        62    0                                            2          4     hr        42    0                                            3          4     hr        37    0                                            4          4     hr        18    0                                            5          1     wk        82    0                                            6          1     wk        65    0                                            7          2     wk        61    0                                            8          2     wk        10    0                                            9          4     wk        76    0                                            10         4     wk        27    0                                            11         4     wk        13    0                                            12         4     wk        4     0                                            13         8     wk        6     0                                            14         8     wk        0     0                                            15         14    wk        3     0                                            16         14    wk        0     0                                            ______________________________________                                    

EXAMPLE 2 Enhancement of Expression by Selective Damage to In SituMesangial Cells

To selectively damage in situ mesangial cells, an anti-mesangial cellmonoclonal antibody, 1-22-3, was used. This antibody recognizes a Thy1-associated molecule on the surface of rat mesangial cells. H. Kawachi,et al., Clin. Exp. Immunol. 88, 399 (1992); H. Kawachi, et al, Clin.Exp. Immunol. 90, 129 (1992). Five hundred μg of a preparation of 1-22-3was injected into the tail vein of 10 rats. Active mesangial cellreplication peaked on days 4-6. H. Kawachi, et al., Clin. Exp. Immunol.88, 399 (1992); H. Kawachi, et al, Clin. Exp. Immunol. 90, 129 (1992).When 1-22-3 antibody was injected into the tail vein, selectivemesangial damage occurred within 24 hours, followed by transient andspecific replication of remnant mesangial cells preceding thereconstruction of normal glomeruli.

RM4/BG715 cells were injected into the left renal artery 3 days afterthe 1-22-3 treatment. Two rats were sacrificed at 4 hours after and at1,2, 4, and 8 weeks after RM4/BG715 cell injection. Renal tissues weresectioned and glomeruli were isolated from each rat as described above.The results of χ-gal assays of the tissues and glomeruli are shown inTable 2. Four hours after cell injection, 43 and 67% of the glomeruli inthe two animals were stained in the χ-gal assay (Table 2). Thepercentage of glomeruli that had detectable β-galactosidase activityremained at 43% or higher among animals sacrificed at 1,2, 4 and 8weeks. In addition, the area of each glomerulus that showed positivestaining in the χ-gal assay increased dramatically between 4 hours and 1week. To quantitate this difference, each χ-gal positive glomerulus wascategorized according to the percentage of glomerular area that wasstained with χ-gal. Four categories were used: 0-5%, 6-25%, 26-50% and51-100%. The percentages of χ-gal positive glomeruli in each of the fourcategories are shown in Table 2. None of the χ-gal positive glomeruliwere stained over a majority (51 to 100%) of the glomerular area at 4hours after injection. At 1, 2, 4 and 8 weeks after injection, at least16%, and up to 63%, of the χ-gal positive glomeruli stained blue over amajority of the glomerular area.

To further quantitate the increased expression in kidneys treated with amesangiolytic agent, an χ-gal score for each animal was calculated usingthe following formula:

    χ-gal score=[(0.025a)+(0.150b)+(0.375c)+(0.750d)][% χ-gal positive glomeruli];

where: a=percentage of χ-gal positive glomeruli in the 0-5% category,b=percentage of χ-gal positive glomeruli in the 6-25% category,c=percentage of χ-gal positive glomeruli in the 26-50% category andd=percentage of χ-gal positive glomeruli in the 51-100% category.

As shown by the χ-gal scores in Table 2, rats sacrificed at 1 week haddramatically increased β-galactosidase activity in situ compared to ratssacrificed at 4 hours. The increased β-galactosidase activity wasobserved at 2, 4 and 8 weeks, as indicated by the χ-gal scores. χ-galscores at 1, 2, 4 and 8 weeks were 6-fold to 15-fold higher than themean χ-gal score at 4 hours (Table 2). These results show that highlevel β-galactosidase expression was maintained throughout the course ofthe experiment. As expected, χ-gal staining was not detected in otherportions of the injected kidneys or in the contralateral kidneys.Selectively damaged rat kidneys that were injected with RM4-4 cellsinstead of RM4/BG715 cells did not have any χ-gal positive staining(data not shown).

                                      TABLE 2                                     __________________________________________________________________________    Percentage of X-gal positive glomeruli in rat left kidneys after              mesangiolytic treatment                                                       and RM4/BG715 cell injection                                                          X-gal                                                                              Percent of X-gal positive                                                positive                                                                           glomeruli having an   Fold                                               glomeruli                                                                          X-gal positive area of:                                                                         X-gal                                                                             increase in                                Animal                                                                            Time                                                                              (%)  0-5%                                                                              6-25%                                                                             26-50%                                                                             51-100%                                                                            score                                                                             X-gal score                                __________________________________________________________________________    17  4 hr                                                                              67   81  16   3    0    372                                                                              --                                         18  4 hr                                                                              43   84  14   2    0    213                                                                              --                                         19  1 wk                                                                              72   15  51  18   16   1928                                                                              6.6                                        20  1 wk                                                                              66   14  18  18   50   3122                                                                              10.7                                       21  2 wk                                                                              83    9  12  20   59   4463                                                                              15.3                                       22  2 wk                                                                              78   10  15  21   54   3968                                                                              13.6                                       23  4 wk                                                                              47    6  12  19   63   2647                                                                              9.0                                        24  4 wk                                                                              43   17  15  31   37   1808                                                                              6.2                                        25  8 wk                                                                              81    6  19  21   54   4162                                                                              14.2                                       26  8 wk                                                                              58   23  15  22   40   2382                                                                              8.1                                        __________________________________________________________________________

These results show that the proportion of cultured mesangial cells in akidney is increased by selectively damaging in situ mesangial cells.Further, the amount of a gene product produced by injected mesangialcells is increased by this method.

EXAMPLE 3 Administration of Cultured Mesangial Cells Prior toSelectively Damaging In Situ Mesangial Cells

RM4/BG715 mesangial cells were injected into the left renal artery ofrats as described above. Three days later, monoclonal antibody 1-22-3was injected into the tail vein of each rat. Two weeks after cellinjection, rats were sacrificed and χ-gal assays carried out asdescribed. In this experiment there was a 4.2 fold increase in the χ-galscore at two weeks when compared to the χ-gal score 4 hours afterRM4/BG715 injection.

EXAMPLE 4 Use of Replication-Defective Mesangial Cells for Site-DirectedGene Delivery

To evaluate the effects of cultured mesangial cell proliferation onamplification of the transfected gene as well as on acceleration ofglomerular injury, behavior of mitomycin C-treated RM4/BG715 cells wasevaluated. In vitro, mitomycin C treatment inhibited the proliferationof RM4/BG715 cells irreversibly but did not affect expression ofβ-galactosidase during a 4-week period of observation.

RM4/BG715 cells were treated with 0.2 μg/ml of mitomycin C (Sigma) for20 hours and then administered to the regenerating kidney according tothe methods set out in Example 2, above. Control cells constitutedRM4/BG715 cells not treated with mitomycin C (untreated cells). After 7days, expansion of χ-gal-positive areas was completely suppressed inthose glomeruli receiving mitomycin C-treated cells, in contrast tothose glomeruli receiving untreated cells. The χ-gal-positive area ineach glomerulus was 2.8±0.1% (mean±SE) in the group receiving treatedcells (n=4) vs. 27.5±5.2 in the group receiving untreated cells (n=5).The renal χ-gal score (see Example 2, above) was 61±21 for the treatedcell group and 2014±288 for the untreated cell group.

Histological analysis revealed that accelerated glomerular injuryinduced by replication-competent cells was limited in the case ofmitomycin C-treated cells. With the replication-defective cells, noevidence of progressive glomerulosclerosis was detected even after 4weeks, when expression of μ-galactosidase was still detected in 11±3.5%(mean±SE, n=4) of glomeruli.

The foregoing detailed description is provided for a betterunderstanding of the invention only and no unnecessary limitation shouldbe understood therefrom as some modifications will be apparent to thoseskilled in the art without deviating from the spirit and scope of theappended claims.

What is claimed is:
 1. A method of expressing a gene product in at leastone of the two kidneys of a mammal, each said kidney having in situmesangial cells in glomeruli and supplied by a renal artery, comprisingthe steps of:(a) providing a plurality of cultured mesangial cells, saidcultured mesangial cells being syngeneic or allogeneic with respect tosaid mammal and containing a nucleic acid expresion comprising asequence encoding said gene product; and (b) administering said culturedmesangial cells to at least one of said renal arteries under conditionswherein said cultured mesangial cells become entrapped in said glomeruliof said kidney supplied by said at least one renal artery and expresssaid gene product.
 2. A method according to claim 1, wherein saidnucleic acid construct further comprises a sequence from areplication-defective retrovirus vector.
 3. A method according to claim1, wherein said gene product is expressed and secreted and enters thecirculatory system, interstitial space, or urinary tract of said mammal.4. A method according to claim 1, wherein said gene product is expressedand is localized in the kidney of said mammal.
 5. A method according toclaim 4, wherein said gene product is expressed and is localized on thecell surface of said mesangial cells.
 6. A method according to claim 1,wherein said exogenous gene comprises a Moloney murine leukemia viruslong terminal repeat.
 7. A method according to claim 1, wherein saidadministering step comprises administering a plurality of said culturedmesangial cells to both of said renal arteries of said mammal, saidcultured mesangial cells becoming entrapped in said glomeruli of bothsaid kidneys and expressing said gene product in both said kidneys.
 8. Amethod according to claim 1, further comprising the step of selectivelydamaging said in situ mesangial cells of said at least one kidney with amesangiolytic agent comprising an anti-mesangial cell antibody.
 9. Amethod according to claim 8, wherein said selectively damaging stepoccurs prior to said administering step.
 10. A method according to claim8, wherein said anti-mesangial cell antibody is a monoclonal antibody.11. A method according to claim 8, wherein said cultured mesangial cellsare replication-defective cells.
 12. A method according to claim 1 or 8,wherein said cultured mesangial cells are autologous to said mammal.